
Variable origindestination trip matrix estimation: A maximum entropyleast squares estimator
Wed, Mar 23, 2011 @ 02:00 PM  03:00 PM
Sonny Astani Department of Civil and Environmental Engineering
Conferences, Lectures, & Seminars
Speaker: Chi Xie, The University of Texas at Austin
Talk Title: Variable origindestination trip matrix estimation: A maximum entropyleast squares estimator
Abstract: In transportation subnetworksupernetwork analysis, it is well known that the origindestination (OD) flow table of a subnetwork is not only determined by trip generation and distribution, but also by traffic routing and diversion, due to the existence of internalexternal, externalinternal and externalexternal flows. This result indicates the variable nature of subnetwork OD flows. This talk presents a variable OD flow table estimation problem for subnetwork analysis. The underlying assumption is that each cell of the subnetwork OD flow table contains an elastic demand function rather than a fixed demand rate and the demand function can properly capture traffic diversion effects under various network changes.
An integrated maximum entropyleast squares (MELS) estimator is proposed, by which OD flows are distributed over the subnetwork so as to maximize the trip distribution entropy, while demand function parameters are estimated for achieving the least sum of squared estimation errors. While the estimator is powered by the classic convex combination algorithm, computational difficulties emerge within the algorithm implementation until partial optimality conditions and a column generation procedure are incorporated into the algorithmic framework. Numerical results from applying the integrated estimator to a couple of subnetwork examples show that a variable OD flow table, when used as input for subnetwork flow evaluations, reflects network flow changes significantly better than its fixed counterpart.
Host: Sonny Astani Dept. of Civil and Environmental Engineering
Location: Kaprielian Hall (KAP)  209
Audiences: Everyone Is Invited
Contact: Erin Sigman